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d3.format = function(specifier) {
  var match = d3_format_re.exec(specifier),
      fill = match[1] || " ",
      align = match[2] || ">",
      sign = match[3] || "",
      basePrefix = match[4] || "",
      zfill = match[5],
      width = +match[6],
      comma = match[7],
      precision = match[8],
      type = match[9],
      scale = 1,
      suffix = "",
      integer = false;

  if (precision) precision = +precision.substring(1);

  if (zfill || fill === "0" && align === "=") {
    zfill = fill = "0";
    align = "=";
    if (comma) width -= Math.floor((width - 1) / 4);
  }

  switch (type) {
    case "n": comma = true; type = "g"; break;
    case "%": scale = 100; suffix = "%"; type = "f"; break;
    case "p": scale = 100; suffix = "%"; type = "r"; break;
    case "b":
    case "o":
    case "x":
    case "X": if (basePrefix) basePrefix = "0" + type.toLowerCase();
    case "c":
    case "d": integer = true; precision = 0; break;
    case "s": scale = -1; type = "r"; break;
  }

  if (basePrefix === "#") basePrefix = "";

  // If no precision is specified for r, fallback to general notation.
  if (type == "r" && !precision) type = "g";

  type = d3_format_types.get(type) || d3_format_typeDefault;

  var zcomma = zfill && comma;

  return function(value) {

    // Return the empty string for floats formatted as ints.
    if (integer && (value % 1)) return "";

    // Convert negative to positive, and record the sign prefix.
    var negative = value < 0 || value === 0 && 1 / value < 0 ? (value = -value, "-") : sign;

    // Apply the scale, computing it from the value's exponent for si format.
    if (scale < 0) {
      var prefix = d3.formatPrefix(value, precision);
      value = prefix.scale(value);
      suffix = prefix.symbol;
    } else {
      value *= scale;
    }

    // Convert to the desired precision.
    value = type(value, precision);

     // If the fill character is not "0", grouping is applied before padding.
    if (!zfill && comma) value = d3_format_group(value);

    var length = basePrefix.length + value.length + (zcomma ? 0 : negative.length),
        padding = length < width ? new Array(length = width - length + 1).join(fill) : "";

    // If the fill character is "0", grouping is applied after padding.
    if (zcomma) value = d3_format_group(padding + value);

    if (d3_format_decimalPoint) value.replace(".", d3_format_decimalPoint);

    negative += basePrefix;

    return (align === "<" ? negative + value + padding
          : align === ">" ? padding + negative + value
          : align === "^" ? padding.substring(0, length >>= 1) + negative + value + padding.substring(length)
          : negative + (zcomma ? value : padding + value)) + suffix;
  };
};

// [[fill]align][sign][#][0][width][,][.precision][type]
var d3_format_re = /(?:([^{])?([<>=^]))?([+\- ])?(#)?(0)?([0-9]+)?(,)?(\.[0-9]+)?([a-zA-Z%])?/;

var d3_format_types = d3.map({
  b: function(x) { return x.toString(2); },
  c: function(x) { return String.fromCharCode(x); },
  o: function(x) { return x.toString(8); },
  x: function(x) { return x.toString(16); },
  X: function(x) { return x.toString(16).toUpperCase(); },
  g: function(x, p) { return x.toPrecision(p); },
  e: function(x, p) { return x.toExponential(p); },
  f: function(x, p) { return x.toFixed(p); },
  r: function(x, p) { return d3.round(x, p = d3_format_precision(x, p)).toFixed(Math.max(0, Math.min(20, p))); }
});

function d3_format_precision(x, p) {
  return p - (x ? 1 + Math.floor(Math.log(x + Math.pow(10, 1 + Math.floor(Math.log(x) / Math.LN10) - p)) / Math.LN10) : 1);
}

function d3_format_typeDefault(x) {
  return x + "";
}

// Apply comma grouping for thousands.
var d3_format_group = d3_identity;
if (d3_format_grouping) {
  var d3_format_groupingLength = d3_format_grouping.length;
  d3_format_group = function(value) {
    var i = value.lastIndexOf("."),
        f = i >= 0 ? "." + value.substring(i + 1) : (i = value.length, ""),
        t = [],
        j = 0,
        g = d3_format_grouping[0];
    while (i > 0 && g > 0) {
      t.push(value.substring(i -= g, i + g));
      g = d3_format_grouping[j = (j + 1) % d3_format_groupingLength];
    }
    return t.reverse().join(d3_format_thousandsSeparator || "") + f;
  };
}
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